Usually, to control the taxiing speed of an aircraft, the pilot has gas control handles (designed to directly control the thrust generated by the engines of the aircraft) and brake pedals (designed to directly control the pressure applied in the wheel brakes).
The pilot of the aircraft is therefore able to act directly on the engine speed and on the braking pressure. These two types of control are obviously separate and must be controlled individually. The result is a significant piloting workload in order to be able to maintain or obtain a desired taxiing speed, and a non-optimal use of the engines and the brakes (premature wear, fuel consumption, etc).
In practice, in addition to generating a significant piloting activity when taxiing, this usual solution presupposes a sometimes excessive use of the actuators (relating to the engines and the brakes) which can bring about an increase in the wear or an unwanted increase in the brake temperatures (with a direct impact on stopover times in certain conditions).